Cenozoic ridge subduction and the resultant slab windows have been well documented worldwide, especially along the western margins of North and South America. The principal characteristics of ridge subduction, which can be used to recognize the process in ancient orogens, include intrusion of ridge-generated magmas into a forearc in a near-trench position; this can be regarded as the hallmark of ridge subduction. The key magmatic products are adakites that include plutonic and volcanic rocks with intermediate- to high-SiO 2 , high Sr/Y and La/Yb ratios, elevated MgO, Na 2 O, K 2 O, Ni and Cr contents, and high LILE and LREE elements. They range from hornblende/biotite-bearing high-Mg diorites , and granodiorites to hornblende/pyroxene high-Mg andesites . They are typically associated with a wide variety of coeval and compositionally diverse volcanic and plutonic rocks such as high-Ca boninites , tholeiitic, high-T basalts , alkaline basalts, charnockites , peraluminous TTGs , I-type granites, and mid-ocean ridge (MOR) (not supra-subduction) ophiolites . The trace element chemistry of these rocks demonstrates that they were generated by partial melting of dehydrated subducted oceanic crust and of lower continental crust , contaminated and metasomatized by juvenile melts that originated by upwelling of asthenospheric mantle. It is this combination of mixed sources that gives rise to the diagnostic and distinctive features of coeval and associated ridge subduction rocks in a near-trench environment. Other important features of ridge subduction are high-temperature metamorphism closely associated with near-trench plutons created by heat released through a slab window, and porphyry gold-copper-zinc mineralization associated with MOR ophiolites and generated in hydrothermal vents at a MOR. When a ridge subducts under a continental margin , the diverging plates associated with the ridge continue to separate creating a slab window that forms between the separating plates. Adakitic melts tend to be generated close to the ...